(1) Special field of the invention
The invention relates to a process and an apparatus for the continuous burning of a fuel in the case of which the fuel is run into a combustion space, in which, after being ignited, it is burnt using oxygen-containing gas run into the combustion space and the relation of gas to fuel is charged so as to be dependent on the control of a desired oxygen content in the flue gas current.
(2) The prior art
In the case of past designs of burner systems, medium is jetted or sprayed into a combustion space, using a nozzle head and burnt, after ignition, using oxygen let into the combustion space. For running in the oxygen, air is sucked using a separate blower and forced into the combustion space (so-called "burner air"). The burner air has to have a certain relation to the heating value of the fuel used in the special case on hand (air relation number) to make certain of the desired combustion.
In this respect burner systems of the prior art make use of compound automatic control with respect, on the one hand, to the amount of fuel run in and, on the other, the amount of air or oxygen used. The desired compound values are, in each case, fixed using mechanical compound automatic controllers. Because, however, the heating value of a certain fuel is not able to be truly classified at the time of combustion, it is never possible to say certainly that at the time of combustion itself the value of the fuel will not be different to the average heating or burning value, for which the adjustment of the system has been made. This is true for all fuels, that is to say, as well, for natural gas and gas coming through long-distance pipelines. In order, even with these chances of having different values, to make certain of keeping up continuous combustion, in burner systems of the prior art operation takes place with excess air to make certain that combustion does not take place under substoichiometric conditions. However, even the use of such excess air all the time makes for many effects which are undesired: for example the sucked-in ballast air (that is to say the oxygen which is run into the combustion space in addition for reasons of safe operation and which may not be burnt), is heated and moved past all heating faces and then goes out of the system as an increased emission factor. A further undesired event is that in the "firing space" (radiation combustion chamber) the flame temperature is lowered by the presence of such excess air with the outcome that there is a marked decrease in the desired heat transmission in the producing or heating system. For these reasons it has furthermore not so far been possible for several fuels to be burnt at the same time in a given firing system with compound automatic controllers; all "combination burners" have an "all or none" operation unit. For this reason the apparatus is made markedly more complex and there are shortcomings with respect to safe operation and in the engineering side of operation; if a combination firing system, generally run on a certain fuel and only designed with a connection for an other fuel to make for safe running, is, after a long time, started up with the other fuel, then it will be seen that, because of the long time in which this other fuel has not been used, trouble will be in some cases very likely, more specifically with respect to the mechanical side of automatic control (cocks, pumps, etc.).
Furthermore, in the case of power stations of great size, it is old for oxygen analyzers to be used in the flue gas duct coming after the combustion process. Using these analyzers, the compound automatic controllers, (which are used because the air rate is dependent on the fuel rate, and not the other way round) undergo adjustment with a moving servo-member for automatic control of the excess air (while keeping to an unchanging combustion power) with an unchanging input rate of fuel. Because, however, volumetric control of gas currents is not readily possible and a, generally speaking, long automatic control lag is necessary in this case, this old process for adjustment of the (mechanical) compound automatic controller may only be used on a very limited scale with good effect in fullsize plant. The base-teaching used so far of an unchanging fuel input rate (or keeping to an unchanging, desired power) and the running in of further air as needed with a marked air excess, was kept to in this old process as well.